1. Technical Field
The present invention relates to a display device, and particularly relates to a liquid crystal display device having a touch screen.
2. Related Art
As a liquid crystal display device can be made compact and slimline, applications are expanding into various fields. A mobile telephone, a PDA, and the like, are examples thereof. In these apparatus, a method wherein a touch screen is used as an input device is expanding. Although there is a static capacitance coupling type, a resistance type, and the like, of touch screen, a configuration in which a resistance type touch screen is used as an input device of a liquid crystal display device is described in JP-A-2005-38231.
In JP-A-2005-38231, a configuration is described in which, by using the same flexible wiring substrate as a flexible wiring substrate which connects the touch screen and an external circuit, and a flexible wiring substrate which connects a liquid crystal display panel and the external circuit, a component cost of a connection with the external circuit is reduced. Also, in JP-A-2005-38231, a configuration is described in which, by using the flexible wiring substrate folded back, an overall size of the display device is reduced.
FIG. 10 is a schematic view of a heretofore known liquid crystal display device with touch screen. In FIG. 10, a resistance, a capacity, and the like, for a position detection being formed in a touch screen 50, a flexible wiring substrate 70, for connecting to a detection circuit for determining a position, is connected.
Meanwhile, a flexible wiring substrate 70 is attached to a liquid crystal display panel 30 in order to supply a power source, and supply an image signal to a pixel. Consequently, to date, both the flexible wiring substrate 70 for the touch screen 50, and the flexible wiring substrate 70 for the liquid crystal display panel 30, have been necessary.
A configuration which, not using a flexible wiring substrate 70 for each of the touch screen 50 and the liquid crystal display panel 30, shares the flexible wiring substrate 70 for the touch screen 50 and the flexible wiring substrate 70 for the liquid crystal display panel 30, is as in FIG. 11. FIG. 11 is the same as the technology described in JP-A-2005-38231. In JP-A-2005-38231, the flexible wiring substrate 70 which connects the touch screen 50 and the liquid crystal display panel 30 extends in a direction perpendicular to the plane of the figure, connecting with an external circuit.
In FIG. 11, the touch screen 50 is configured of a front surface conductive layer 52, and a substrate. A protection layer 53 is formed on a front surface of the conductive layer 52. Although the touch screen 50 of JP-A-2005-38231 is a resistance type touch screen 50, FIG. 11 is a capacitive touch screen 50. The liquid crystal display panel 30 is configured of a TFT substrate 10, on which are formed pixel electrodes, thin film transistors (TFT's), image signal wires, scan signal wires, and the like, a color filter substrate 20, on which is formed a color filter and the like, and a liquid crystal layer sandwiched by the TFT substrate 10 and the color filter substrate 20.
A problem with the configuration shown in FIG. 11 is as follows. That is, a human touches the touch screen 50 with a finger, a touch screen 50 pen, or the like, but on being touched a large number of times, the thin protection layer 53 tears, the conductive layer 52 also tears, and the touch screen 50 ceases to function.
Another problem with the configuration shown in FIG. 11 is as follows. That is, as the liquid crystal display panel 30 is not light-emitting, a backlight 40 is necessary in order to display an image. With the kind of configuration of FIG. 11, a light L from the backlight 40 firstly, unlike with a regular liquid crystal display device, falls incident on the color filter substrate 20. Subsequently, a transmitted light is emitted, via the TFT substrate 10, on a touch screen 50 side.
With this kind of configuration, as a human sees an image from a TFT substrate 10 side, a contrast of the image deteriorates. That is, although it is possible to form a black matrix in order to raise the contrast on a color filter substrate 20 side, it is difficult to form a black matrix on the TFT substrate 10 side.